This is a spin-off story of the manga GTO(Great Teacher Onizuka). This takes place directly after the Teshigawara arc[after he was shot by him]

After Eikichi Onizuka was shot by the former teacher Teshigawara, he was sent to the hospital. Shortly afterwards he escaped, then disapeared for 14 days after an incident involving a t.v. appearance. Strangely enough, when he returned, a wanted poster appeared with a man that resembled very much like Onizuka. What exactly did he do during those 14 days?

http://www.mangafox.com/manga/great_teacher_onizuka/ - Original series

The series GTO: Shonan 14 Days has been licensed, it is not available in Manga Fox.